Implement overlay scrollbar fade out for non-composited scrollers.

third_party/WebKit/Source/platform/scroll/ScrollbarTheme.cpp

 /*
  * Copyright (C) 2011 Apple Inc. All Rights Reserved.
  *
  * Redistribution and use in source and binary forms, with or without
  * modification, are permitted provided that the following conditions
  * are met:
  * 1. Redistributions of source code must retain the above copyright
  *    notice, this list of conditions and the following disclaimer.
  * 2. Redistributions in binary form must reproduce the above copyright
  *    notice, this list of conditions and the following disclaimer in the
@@ skipping 215 matching lines @@
 bool ScrollbarTheme::shouldSnapBackToDragOrigin(
     const ScrollbarThemeClient& scrollbar,
     const PlatformMouseEvent& evt) {
   IntPoint mousePosition = scrollbar.convertFromRootFrame(evt.position());
   mousePosition.move(scrollbar.x(), scrollbar.y());
   return Platform::current()->scrollbarBehavior()->shouldSnapBackToDragOrigin(
       mousePosition, trackRect(scrollbar),
       scrollbar.orientation() == HorizontalScrollbar);
 }
 
+double ScrollbarTheme::overlayScrollbarFadeOutDelaySeconds() const {
+  // On Mac, fading is controlled by the painting code in ScrollAnimatorMac.
+  return 0.0;
+}
+
+double ScrollbarTheme::overlayScrollbarFadeOutDurationSeconds() const {
+  // On Mac, fading is controlled by the painting code in ScrollAnimatorMac.
+  return 0.0;
+}
+
 int ScrollbarTheme::thumbPosition(const ScrollbarThemeClient& scrollbar,
                                   float scrollPosition) {
   if (scrollbar.enabled()) {
     float size = scrollbar.totalSize() - scrollbar.visibleSize();
     // Avoid doing a floating point divide by zero and return 1 when
     // usedTotalSize == visibleSize.
     if (!size)
       return 0;
     float pos = std::max(0.0f, scrollPosition) *
                 (trackLength(scrollbar) - thumbLength(scrollbar)) / size;
@@ skipping 135 matching lines @@
       return DisplayItem::kScrollbarBackTrack;
     case ForwardTrackPart:
       return DisplayItem::kScrollbarForwardTrack;
     default:
       ASSERT_NOT_REACHED();
       return DisplayItem::kScrollbarBackTrack;
   }
 }
 
 }  // namespace blink